Atomic and Molecular Physics
and
Quantum Chemistry
meeting of the 14th AIP Congress
Adelaide, South Australia
Tuesday 12 - Friday 15 December 2000
local organisers: Michael Brunger and Igor Bray


The present plan for the meeting is to have twelve 30 minute invited talks. The remainder of the program will consist of up to 48 self-invited 15 minute contributions, as well as posters.
To be determined: Rooms for talks and posters, and presentation facilities.

Friday 15th, 9:45 am, Plenary speaker: Prof. Chris Greene, University of Colorado, Boulder, Colorado, USA
 Title: Photoionization of light atoms and molecules: A window into few-body and many-body dynamics
Abstract: Species as simple as atoms and molecules with two or three electrons continue to provide surprises and challenges, while resisting a full quantitative description. The past few years have seen tremendous progress. Numerous long-existing roadblocks have been overcome by theorists, as well as experimentalists working on a number of different fronts. This is an exciting time, because theoretical capabilities have improved dramatically. We can now describe complicated resonant photoionization processes in helium or molecular hydrogen that seemed inconceivable in the early 1990s. While nonresonant ejection of two electrons in these species by a single energetic photon seems unlikely, from an independent particle perspective, it can be surprisingly important. My talk will give an overview of recent progress, and will address some of the regimes where we still need to achieve a better understanding.

Speakers, 25 mins + 5 mins question time:
    Chair: Michael Brunger
  1. Tuesday 12th, 11:00 am, Birgit Lohmann, Griffith University: Ionization of heavy rare gases - a challenge to theory.
  2. Tuesday 12th, 11:30 am, Helen Dorsett, Defence Science and Technology Organisation, Salisbury: Detonation Chemistry.
    3. The sensitivity of carbon-based 'high' explosives to unintentional initiation is a matter of increasing international concern, due in part to the existence of large stockpiles of aging nuclear weapons. The sensitivity of an explosive is related to the early stages of its decomposition, and can therefore be modelled by first-principles quantum chemistry. This talk will discuss some general approaches to modelling initiation of reaction to detonation in solid explosives and their application to real systems, in particular, 1,1-diamino-2,2-dinitroethylene, a recently-synthesised insensitive explosive, and triaminotrinitrobenzene (the explosive initiator in nuclear weapons).
  3. Tuesday 12th, 12:00 pm, Bill MacGillivray, Griffith University: New electron-atom collision experiments involving lasers.
    4. The development of single mode lasers has opened up opportunities to study electron-atom collision processes, some of which have previously been inaccessible. Laser radiation can be used to prepare an atom in a particular state prior to collision, to interrogate the state of the atom following collision or to assist the electron in exciting a transition. In this talk, several new studies of electron-atom collisions involving lasers at Griffith University will be described.
    Lunch break, 12:30 pm
    Chair: Peter Teubner
  4. Thursday 14th, 11:00 am, Gerard Milburn, University of Queensland: Quantum phase transitions in an ion trap.
    5. We show how a conditional displacement of the vibrational mode of trapped ions can be used to simulate nonlinear collective and interacting spin systems including nonlinear tops and Ising models (a universal two qubit gate), ndependent of the vibrational state of theion. Thus cooling to the vibrational ground state is unnecessary provided the heating rate is not too large.
  5. Thursday 14th, 11:30 am, Victor Flambaum, University of New South Wales: Do fundamental constants vary with time and distance?
    6. Were the laws of nature the same ten billion light years away from us? A change in the fine structure constant alpha could be detected via shifts in the rest wavelengths of resonance transitions in quasar absorption systems. We have developed a new approach which improves the sensitivity of this method by an order of magnitude (the effect that we study is 10 times larger than that studied in the previous works, see Phys. Rev. Lett. 82, 888, 1999). We have measured the fine structure constant in 49 absorption systems covering look-back times from 0.2 to 0.9 times the age of the Universe. Theories unifying gravity with other interactions predict the spatial and temporal variation of the fundamental "constants" in the Universe. Current interest is high because in superstring theories, which have additional spatial dimensions compactified on tiny scales, any variation of the mean size of the extra dimensions results in changes of the 3-dimensional observed coupling constants. Also, we can now probe variations at the level predicted in inflationary models of the Universe. Our initial results hinted that alpha may have been smaller in the past (Phys. Rev. Lett., 82, 884, 1999). Startlingly, new results based on independent data support the same effect.
  6. Thursday 14th, 12:00 pm, Victor Karaganov, Flinders University: Superelastic scattering of electrons from laser excited alkali atoms.
    7. Lunch break, 12:30 pm
    Chair: Igor Bray
  7. Friday 15th, 11:00 am, Andris Stelbovics, Murdoch University:How to calculate electron-atom ionisation.
    8. The last couple of years have been particularly interesting because our understanding of what is required to solve the Schrödinger equation for electron-impact ionisation has increased significantly. In the difficult intermediate energy region, ionisation has been modelled with considerable success by adaptation of the convergent close coupling equations. More recently "direct" methods that are based on the solution of the second-order time-independent coordinate-space Schrödinger equation have come to the fore. In these methods treatment of ionisation boundary conditions is transparent but they are computationally intensive. In this talk I will compare the various approaches and indicate the directions they are taking us.
  8. Friday 15th, 11:30 am, Anatoli Kheifets, Australian National University: Two-electron photoionization from correlated atomic targets
  9. Friday 15th, 12:00 pm, Jamal Berakdar, Halle, Germany: Two-particle wave function engineering.
    10. Nano and mesoscopic semiconductor quantum dots (QDs), equally called "artificial atoms", are systems in which the charge carriers are confined in all directions to characteristic lengths comparable to the de Broglie wave length of the particles. The extremely versatile nature of QDs make them an appealing candidate both for applied and fundamental research. E.g., parameters such as particle number and charge density can be experimentally varied in regions not accessible in atomic or molecular systems which renders possible a detailed study of correlation and confinement effects. In this theoretical work we develop concepts for the description of many-body and interaction effects in few-electron QDs. The method is based on the many-body Green function techniques and on a recently developed reduction scheme for the many-body Green operators in terms of lower dimensional Green operators. We also investigate QDs in strong laser fields and derive the time-dependent many-body wave function by means of path integral methods. Experimentally, the properties of QDs can be explored by optical methods such as multi excitation and single photoemission spectroscopy. Here we propose in addition the one-photon double emission (PDE) of QDs as a tool to investigate correlation and quantum size effects. We evaluate the DPE transition amplitude using the two-particle Green operator to propagate the two-particle ground state to the photo-excited one. Results, that will be presented at the conference, are very sensitive to the size of the dot and to the way the electronic correlations are modelled.
    Lunch break, 12:30 pm
    Chair: Birgit Lohmann
  10. Friday 15th, 2:00 pm, Peter Hammond, University of Western Australia: Radiative decay of doubly excited states
  11. Friday 15th, 2:30 pm, Maarten Hoogerland, Australian National University: Electron scattering from laser cooled metastable helium atoms.
  12. Friday 15th, 3:00 pm, Harry Quiney, University of Melbourne: Relativistic molecular quantum electrodynamics: light, and the heavy elements. The importance of relativistic effects in atomic physics is well-established, where theoretical modelling plays an important role in the design of lighting, optical and plasma devices, as well as in the analysis of high-precision experimental spectroscopy. There has been very significant recent activity in the implementation of relativistic electronic structure methods for molecules and small clusters containing heavy elements, requiring the development of new approaches to meet the computational challenges which these systems present. This presentation will survey the incidence of relativistic effects in atoms and molecules, both in the structural characteristics of these systems and in their interactions with external fields. Our computational scheme for calculating atomic and molecular structures based on relativistic quantum electrodynamics will be described in the context of applications to the high-precision spectroscopy of small molecules. Future directions of this work, towards the development of relativistic convergent-close-coupled methods for electron-atom and electron-molecule scattering, and the modelling of environmentally hazardous actinide compounds will also be discussed.
    13. End of session, 3:30 pm

Speakers, 12 mins + 3 mins question time:
    Chair: Bill MacGillivray
  1. Tuesday 12th, 2:00 pm, Robert Sang, Griffith University:
    2. Total absolute electron-metastable neon collision cross section measurements via a magneto-optical trap. The measurement of accurate absolute total differential electron-atom collision cross sections is important to test fundamental scattering theories describing these processes [1]. Many devices from the fluorescent lamp to the helium-neon laser rely on metastable atom collisions, and as such, the data obtained from more accurate absolute total cross section measurements could produce more efficient devices. In this paper we will present an experimental technique based on the pioneering work of the group of Lin and coworkers [1,2] that utilises a magneto-optical trap for atoms in the 2P3/23s[3/2]2 metastable state of neon for the measurement of total absolute collision cross sections. The technique allows the determination of these cross sections without the knowledge of target density. We will present the progress of new absolute total collision cross sections measurements using these techniques using a new experimental apparatus that produces a bright beam of laser-cooled metastable neon.
    [1] R.S. Schappe, P. Feng, L.W. Anderson, C.C. Lin, and T. Walker, Euro. Phys. Lett. 29, 439, 1995.
    [2] R.S. Schappe, T. Walker, L.W. Anderson ,and C.C. Lin, Phys. Rev. Lett. 76, 4328, 1996.
  2. Tuesday 12th, 2:15 pm, David Waterhouse, University of Western Australia:
    3. Long-range Coulomb interactions in low energy (e,2e) Data. Proper treatment of long-range Coulomb interactions has confounded atomic collision theory since Schrödinger first presented a quantum-mechanical model for atomic interactions. The long-range Coulomb interactions are difficult to include in models in a way that treats the interaction sufficiently well but at the same time ensures the calculation remains tractable. An innovative application of an existing multi-parameter (e,2e) data acquisition system will be described. To clarify the effects of long-range Coulomb interactions, we will report the correlations and interactions that occur at low energy, observed by studying the energy sharing between outgoing electrons in the electron-impact ionisation of krypton.
  3. Tuesday 12th, 2:30 pm, Julian Lower, Australian National University:
    4. (e,2e) Collisions with Polarized Electrons and Excited, Oriented and Spin Polarized Targets. We present state resolved (e,2e) studies on the ionization of ground and laser excited sodium atoms. In these measurements the angular momentum projection state of both projectile and target is determined prior to collision, degeneracies which are averaged over in conventional measurements. The results are compared to Distorted Wave Born Approximation (DWBA) and Dynamically Screened Three Coulomb Waves (DS3C) scattering calculations. Aided by the introduction of four tensorial parameters, the study provides insight into mechanisms by which angular momentum is transferred from the initial bound state to the two final state continuum electrons in both singlet and triplet spin channels.
  4. Tuesday 12th, 2:45 pm, Matthew Haynes, Griffith University:
    5. Low energy electron impact ionization measurements of argon in coplanar symmetric and asymmetric geometries. We report here on our most recent electron-electron coincidence experiments for ionization of the 3s and 3p orbitals in argon (binding energy of 29.3 eV and 15.8 eV respectively) at low energies in coplanar symmetric and asymmetric geometries. Comparison will be made with a distorted wave Born approximation calculation.
  5. Tuesday 12th, 3:00 pm, Robert Gulley, Australian National University:
    6. Absolute Electron Scattering from C6H6 and C6F6. We report absolute differential cross section measurements for vibrationally elastic scattering of electrons from benzene (C6H6) and hexafluorobenzene (C6F6). The measurements have been performed in our two laboratories on different crossed-beam apparatuses for scattering angles between 10° and 130° - C6H6 at the Australian National University in the energy range from 1.1 to 40 eV, and C6F6 at Sofia University from 1.5 to 100 eV. The cross sections, which are characterised by strong forward-angle scattering and large-angle oscillations for both molecules, are favourably compared with recent theoretical calculations.
  6. Tuesday 12th, 3:15 pm, Linda Uhlmann, Australian National University:
    7. Absolute Elastic Cross Sections for Electron Scattering from SF6. Absolute differential cross sections for vibrationally elastic scattering of electrons from sulphur hexafluoride (SF6) have been measured at fixed angles of 60°, 90° and 120° over the energy range of 5 to 15 eV, and also at 11 fixed energies between 2.7 and 75 eV for scattering angles between 10° and 180°. These measurements employ the magnetic angle-changing technique of Read and Channing in combination with the relative flow technique to obtain absolute elastic scattering cross sections at backward angles (135° to 180°) for incident energies below 15 eV. The results reveal some substantial differences with several previous determinations and a reasonably good level of agreement with a recent close coupling calculation.
    Tea break, 3:30 pm
    Chair: Andris Stelbovics
  7. Tuesday 12th, 4:00 pm, John Furst , University of Newcastle:
    8. Measuring Zero: How photon polarisation measurements provide an insight into the dynamics of electron scattering from the rare gases. Photon polarisation measurements enable the dynamics of collision processes near threshold to be untangled without resorting directly to complicated calculations. I will discuss the use of symmetry arguments in the prediction of threshold polarisations due to the spin-orbit interaction in the rare gases, and compare the outcomes with more detailed (but certainly not complicated) calculations.
  8. Tuesday 12th, 4:15 pm, Dmitry Fursa, Flinders University:
    9. Electron scattering from the ground state of mercury. Close-coupling calculations have been performed for electron scattering from the ground state of mercury. We have used non-relativistic convergent close-coupling computer code with only minor modifications in order to account for the most prominent relativistic effects. These are the relativistic shift effect and singlet-triplet mixing. Very good agreement with measurements of differential cross sections for elastic scattering and excitation of 6s6p-1-P state at all energies is obtained.
  9. Tuesday 12th, 4:30 pm, Bipina Dhal , University of Melbourne:
    10. Competitive-channel of double Electron Transfer in Ion-Atom Collision. Recent development in the theoretical and experimental studies on electron transfer is highlighted. Validity of single collision condition and isolated atom concept were achieved by gas target measurement. Studies on sub-shell resolved electron transfer for solid targets were also extrapolated to vanishing thicknesses. Predictions of the recently developed theory of a Close Coupling (CC) calculation based on a Two State Atomic Expansion (TSAE) and Continuum Distorted Wave eikonal initial state (CDW-EIS) were compared with the experimental results. The cross-section for the simultaneous transfer of two electrons is comparable to the singe electron transfer cross-sections as the symmetry of the collision system is approached.
  10. Tuesday 12th, 4:45 pm, Alisher Kadyrov , Flinders University:
    11. Convergent close-coupling: extension to the positron-hydrogen system. Difficulties accompanying the generalisation of the convergent close-coupling approach to two-centre scattering problems will be discussed. Recent results obtained for the simple model of positron-hydrogen scattering that retains only states of zero orbital angular momentum will be presented. Status of the full positron-hydrogen calculations will be reported.
  11. Tuesday 12th, 5:00 pm, Anthony J. Blackett , Murdoch University:
    12. Solving the Momentum-Space Lippmann-Schwinger Equation Using a Rotated-Contour Method. Describing target-atom continua via the momentum-space convergent-close-coupling approach is based on the momentum-space Lippmann-Schwinger equation, which is itself, an integral form of Schrödinger's equation. The singular nature of the Green's function in the integral kernel of the momentum-space LS equation makes numerical solutions intrinsically difficult. Standard numerical integration techniques employed to avoid computational problems that occur near the singularity in larger calculations, such as subtraction methods, become more troublesome as the number of channels in the calculation is increased. The rotated-contour method offers the potential of avoiding complications associated with the singularity by performing the momentum integration along a singularity-free contour in the complex momentum plane. The underlying theory of the rotated-contour method will be discussed along with its application to solving the momentum-space LS equation for electron scattering from hydrogen.
    Close,5:15 pm
    Chair: Dmitry Fursa
  12. Thursday 14th, 2:00 pm, Peter Riggs, University of Adelaide:
    13. Quantum Phenomena in Terms of Energy-Momentum Transfer. In the deBroglie-Bohm version of quantum mechanics, the motion of a quantum particle is governed by its wave field which is taken to be a physically real field. It is found that the dynamic role of the wave field is to influence the motion of a quantum particle by means of transferring energy-momentum between particle and field. The particle's energy increases (decreases) with decreases (increases) in the amount of energy stored in the wave field.
  13. Thursday 14th, 2:15 pm, Michael Bromley , Northern Territory University:
    14. Configuration Interaction Calculations of Positronic Atoms and Ions. The Configuration Interaction (CI) method is one of the most commonly used methods for the calculation of the electronic structure of atoms. The standard CI method based on a linear combination of orthonormal orbitals centred on the nucleus has been adapted to the calculation of the structure of exotic atoms containing one or two valence electrons and a positron. Recent results of large scale calculations on a number of systems, including PsH, e+Li, e+Be, e+Mg, e+Ca, e+Cu, e+Zn, e+Sr and e+Cd will be reported. These investigations have highlighted some of the basic conditions required for the 'stable' binding of positrons to neutral atoms.
  14. Thursday 14th, 2:30 pm, Andrey Lugovskoy , Flinders University:
    15. Shake-up of a Light Atom in a Collision with a Hard Wall. Light atom scattering off a hard wall is studied with consideration of electron transitions initiated by the collision. This problem is shown to allow analytical solution when the electron-solid interaction is neglected. The influence of this interaction on the atomic level populations is discussed on the basis of the first Born approximation.
  15. Thursday 14th, 2:45 pm, Ben Travaglione, University of Queensland:
    16. Applying Kitaev's Algorithm in an Ion Trap Quantum Computer. Kitaev's algorithm is a method of estimating eigenvalues associated with an operator. Shor's factoring algorithm, which enables a quantum computer to crack RSA encryption codes, is a specific example of Kitaev's algorithm. It has been proposed that the algorithm can also be used to generate eigenstates. We extend this proposal for small quantum systems, identifying the conditions under which the algorithm can successfully generate eigenstates. We then propose an implementation scheme based on an ion trap quantum computer. This scheme allows us to illustrate a simple example, in which the algorithm effectively generates eigenstates.
  16. Thursday 14th, 3:00 pm, Peter Drummond, University of Queensland:
    17. STIRAP in coupled atomic and molecular superchemistry.
  17. Thursday 14th, 3:15 pm, Chanh Quoc Tran, University of Melbourne:
    18. X-Ray Extended-Range Technique for Precision Measurement of the X-Ray Mass Attenuation Coefficient and IM(F) for Copper Using Synchrotron Radiation.
    Tea break, 3:30 pm
    Chair: Anatoli Kheifets
  18. Thursday 14th, 4:00 pm, Winfried Hensinger , University of Queensland:
    19. Single atom phase space tunneling. We report the latest results from our experiments on phase space tunneling using the dynamics of cold rubidium atoms in an optical lattice. We have succeeded in preparing a superposition of Floquet states which is localised in one resonance. Furthermore we have successfully accomplished access to a regime where the action of motion of the atom inside the well is only ten times larger than Planck's constant indicating the emergence of quantum features on observable short time scales. The observation of resonances was achieved for a modulation length of more than 100 modulation periods.
  19. Thursday 14th, 4:15 pm, Howard Wiseman , Griffith University:
    20. Reducing the Linewidth of an Atom Laser by Feedback. A continuous atom laser will almost certainly have a linewidth dominated by the effect of the atomic interaction energy, which turns fluctuations in the condensate atom number into fluctuations in the condensate frequency. These correlated fluctuations mean that information about the atom number could be used to reduce the frequency fluctuations, by controlling a spatially uniform potential. It turns out that counting atoms in the output of the atom laser is essentially useless for such feedback. However, feedback based on a physically reasonable quantum nondemolition measurement of the atom number of the condensate in situ can reduce the linewidth enormously.
  20. Thursday 14th, 4:30 pm, Jacinda Ginges, University of New South Wales:
    21. Calculation of parity nonconserving s-d transitions in Cs, Fr, Ra II, and Ba II. It is important to calculate parity nonconserving (PNC) electric dipole (E1) transitions because the value of the nuclear weak charge can be extracted by comparison with experiment, providing a unique test of the Standard Model. The benefit of studying s-d transitions over the 6s-7s PNC transiton in cesium, which gives the highest accuracy for the value of the nuclear weak charge, is that there are no strong cancelations between different terms in the sum-over-states approach. If E1 amplitudes are measured to high accuracy, the accuracy of the calculations of PNC s-d amplitudes can be reduced to the order of a fraction of a percent.
  21. Thursday 14th, 4:45 pm, Vladimir Dzuba, University of New South Wales:
    22. Atomic theory and test of the Standard Model. We have performed relativistic many-body calculations of the hyperfine interaction in the 6s and 7s states of Cs, including the off-diagonal matrix element. We have found that in spite of the large value of the many-body effects the off-diagonal matrix element can still be expressed to very high accuracy via the square root of the product of the diagonal matrix elements. The result is used in the interpretation of the parity-violation measurement in the 6s-7s transition in Cs which claims a possible deviation from the Standard Model.
  22. Thursday 14th, 5:00 pm, Chris Chantler , University of Melbourne:
    23. What is wrong with the fundamental constants of nature? Every decade the CODATA recommended values for the fundamental constants are refined to a self-consistent set by P. J. Mohr & B. N. Taylor. The 1998 adjustment reduces uncertainties by factors of five or ten and has been published simultaneously as Rev.Mod.Phys. 72 (2000) 351-495 and J.Phys.Chem.Ref.Data (2000). This presents a detailed review of many superlative experiments, showing dramatic improvements in experiment and theory since the last 1986 adjustment. However, an anomaly showed up in this last adjustment which may suggest that problems in QED are being observed. This situation will be discussed, and possible explanations will be presented, with a view to identifying future critical experiments to resolve the current inconsistencies.
  23. Thursday 14th, 5:15 pm, David Paterson, University of Melbourne:
    24. High-accuracy absolute test of Quantum Electrodynamics for helium-like and hydrogenic vanadium using the NIST electron-beam ion trap. The most accurate measurement of resonance lines in helium-like vanadium are reported. The absolute calibration is achieved by using a spread of characteristic wavelengths to rigorously determine the dispersion function of the spectrometer. Systematic shifts associated with the shape and location of the detector have been reduced dramatically. Results are in agreement with recent theoretical calculations and the experimental precision (0.14 eV) is comparable to the uncertainty in theory. Measurements represent a 5.7%-8% determination of the QED contribution. Recent measurement of Lyman alpha in hydrogenic vanadium is discussed, together with the current status of medium-Z X-ray QED investigations.
    Close,5:30 pm

Friday 15th, 4 pm, Posters:
  1. V. V. Flambaum and J. C. Berengut, University of New South Wales:
    2. Atom made from charged elementary black hole. It is believed that there may have been a large number of black holes formed in the very early universe. These would have quantised masses. A charged ``elementary black hole'' (with the minimum possible mass) can capture electrons, protons and other charged particles to form a ``black hole atom''. We have found the spectrum of such an object with a view to laboratory and astronomical observation of them, and have estimated the lifetime of the bound states. In this system there is also the distinct possibility of single quark capture. This leads to the formation of a coloured black hole that plays the role of an extremely heavy quark interacting strongly with the other two quarks.
  2. Tony Shackleton and Andris T. Stelbovics, Murdoch University:
    3. Failure of the n3 scaling law in the Temkin-Poet model of e-H scattering. We have carried out a study of the Temkin-Poet model of e-H scattering. This model has been of considerable interest to scattering theorists because it is a subset of the full e-H problem and has been used many times to test methods of solution of the full problem. Recently it was shown by Ihra and Macek that the ionisation cross section should be suppressed near threshold. The reason for this is that, classically, ionisation is forbidden in a small region above threshold and hence quantum mechanically we expect a manifestation of quantum mechanical tunnelling. Because the total ionisation cross section can be found using the optical theorem for total cross section and then subtracting off the discrete inelastic scattering cross sections, one might expect interesting behaviour of the inelastic cross sections. Indeed this is confirmed by our extensive numerical simulations using a solution method based on Poet's Fredholm equation of the first kind for the scattering matrix. We conclude that the cross sections fall off at a rate faster than the n3 scaling law in a region of about 2eV below and above the ionisation threshold. The rate varies with nearness to the threshold.
  3. Laurence Campbell, David C Cartwright, Michael J Brunger, Peter J O Teubner and Joanne Harrison, Flinders University:
    4. Vibrational-Electronic Excitation of NO and N2 by Electron Impact. Electron scattering plays a role in radiative transfer in the upper atmosphere, by producing excited states of atoms and molecules, which then undergo radiative decay to the ground state, often cascading through a series of intermediate states. This is modelled by a "statistical equilibrium" between the production of excited states by electron impact and their loss by the radiative cascade and quenching by collisions. We present the results of such a calculation which incorporates cross sections from recent measurements of scattering by nitric oxide and molecular nitrogen, and compare the calculated radiative spectrum with measurements in auroral conditions.
  4. M. R. Went, Griffith University:
    5. Complete Electron Rubidium Collision Experiments. To completely describe S to P electron impact excitation for rubidium, four complex scattering amplitudes are needed. The amplitudes and phases are determined by obtaining information on the state of the atom and the electron following the collision. Equivalently, the time reversed superelastic scattering experiment can be performed in which the atomic state is prepared by single mode laser radiation of known polarisation. The complimentary STU experiment yields information about the polarisation of the electrons following the collision. We will report on the current status of the spin polarised superelastic experiment and discuss our current measurements.
  5. D. H. Yu, University of Western Australia:
    6. Electron exchange in the dissociation and excitation of molecules by polarized electrons. The dissociation and excitation process of the H2, H2O, NH3 and CH4 molecules has been studied by polarised electrons. The electron exchange effects have been observed.
  6. Robert Gulley, Australian National University:
    7. Very Low Energy Electron Scattering in Nitromethane, Nitroethane and Nitrobenzene. We report absolute total integral and total backward scattering cross sections for CH3NO2, C2H5NO2 and C6H5NO2 at incident electron energies from 30 meV to several eV, with some additional data at higher energies. These experimental results provide a test of the validity of the Born point-dipole approximation for the calculation of rotationally inelastic scattering cross sections for polar molecules, of importance in modelling the chemical and physical characteristics of industrial and natural plasmas.
  7. Vladimir Dzuba, V. V. Flambaum, and J. S. M. Ginges, University of New South Wales:
    8. Enhancement of parity and time invariance violation in radium. Parity and time invariance violating effects in radium are strongly enhanced due to the large nuclear charge Z, close electronic states of opposite parity, and the collective nature of P,T-odd nuclear moments. We have calculated the electric dipole moment (EDM) of Ra induced by nuclear P,T-odd moments or the electron EDM as well as parity non-conserving transition amplitudes induced by both nuclear spin-independent (nuclear weak charge) and spin-dependent (anapole moment) weak interactions. The value of these effects are much larger than those considered before in other atoms.
  8. Vladimir Dzuba1, V. V. Flambaum1, G. F. Gribakin2 and C. Harabati1, 1University of New South Wales, 2Queen's University of Belfast:
    9. Calculation of positron binding to copper, silver and gold atoms. Positron binding to copper, silver and gold atoms was studied using a fully ab initio relativistic method, which combines the configuration interaction method with many-body perturbation theory. It was found that the copper and silver atoms form bound states with a positron with binding energies 170 meV for Cu and 123 meV for Ag, while the Au atom cannot bind a positron. Our calculations reveal the importance of the relativistic effects for positron binding to heavy atoms. In the non-relativistic limit positron is bound to all three atoms with very close binding energies of about 200 meV.
  9. Vladimir Dzuba and V. V. Flambaum, University of New South Wales:
    10. Atomic clocks and search for variation of the fine structure constant. Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical constants. Possible time evolution of the fine structure constant alpha can be studied by comparisons of rates between different atomic clocks. The sensitivity to variation of alpha is due to relativistic corrections which vary from atom to atom. We have calculated these corrections for In II, Tl II, Ba II and Ra II ions which can all be used as atomic optical clocks. The results are to be used to translate any change in the clock's rate into variation of alpha.
  10. Victor Flambaum1, G. F. Gribakin2, C. Harabati1 and G. Shaw2, 1University of New South Wales, 2Queen's University of Belfast:
    11. Cold-atom scattering: from the scattering length to the glory oscillations. We show that in a wide range of energies, from threshold to deep into the semiclassical domain, the scattering of atoms can be described in terms of just two large parameters. They are a long-range parameter, determined by the long-range behavior of the interatomic potential and the reduced mass, and a short-range parameter which is the semiclassical s-wave phase at zero energy. The first of these parameters is known quite well. On the other hand, the phase depends on the behavior of the potential at small distances, which is often not known sufficiently accurately.
  11. V. V. Flambaum1, A. A. Gribakina1, G. F. Gribakin2 and C. Harabati1, 1University of New South Wales, 2Queen's University of Belfast:
    12. Chaotic many-body states as a source of strong enhancement of electron recombination with multicharged ions. In this work we consider the problem of recombination of low-energy electrons with multicharged ions (e.g., Au25+) It has been known for a while that in such systems the recombination rates can be much greater than those due to simple single-particle direct radiative recombination (RR).The spectrum and eigenstates of open-shell multicharged atomic ions near the ionisation threshold are chaotic. This complexity enables one to use statistical methods to analyse the system. The calculation starts with the construction of the mean field of the ion Au24+, which is the Dirac-Fock approximation in this work. The single-particle orbitals are then used to calculate properties of many-electron states: the level density, orbital occupation numbers, mean-squared values of transition amplitudes, etc.
  12. Holly Rose, A. G. Mikosza and J. F. Williams, University of Western Australia:
    13. Measurements of Scattering Parameters of the He(3-3-D) and He(4-1,3-F) States. The use of electron-photon and polarised photon-cascade photon coincidence techniques in the investigation of atomic excitation by electron impact is now well established, particularly for the low-lying states (n1S, n1P) of the helium atom. More recently these techniques have been extended to begin looking at higher angular momentum states (e.g. He(31,3D)1). Whilst the basic two particle electron-photon and polarised photon-cascade photon methods can provide some angular and polarisation correlation information on these states, they cannot be used to completely characterise the state. A complete description of these requires the triple coincidence detection of the scattered electron and two cascade decay photons with polarisation analysis of one decay photon. This technique has most recently been used to provide a complete description of the He(31D) state1.

    Efforts are now being directed towards the use of these coincidence techniques for study of the He(33D) and He(41,3F) states. Angular and polarisation correlation measurements on the He(33D) state will be compared with measurements made previously by Crowe et al2 and Cvejanovic et al3 and will also be used to verify the predictions of the convergent close coupling theory of Fursa et al4. The He(33D) is an example of exchange scattering and has not yet been studied in great detail.

    The near energy degeneracy of the He(41F) and (43F) states produces a nearly completely mixed singlet-triplet state and provides a means for investigation into the exchange and coupling mechanisms. Very little coincidence work5 and no triple coincidence studies have been attempted on the He(41,3F) state.

    Progress towards the measurement of the scattering amplitudes and phases of the magnetic sublevels of the He(33D) and He(41,3F) states will be reported.

    1. A.G. Mikosza and J.F. Williams, J. Phys. Aust. 49 (1996) 375
    2. A. Crowe, B.P. Donnelly, D.T. McLaughlin, I. Bray and D.V. Fursa, J Phys B: At. Mol. Opt. Phys. 27 (1994) L795
    3. D Cvejanovic, K Clague, D Fursa, K Bartschat, I Bray and A Crowe, J Phys B: At. Mol. Opt. Phys. 33 (2000) 2265-2278
    4. D. Fursa, I. Bray, B P Donnelly, D T McLaughlin and A Crowe, J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 3459-3473
    5. D. Cvejanovic and A. Crowe, Phys. Rev. Lett. 80 (1988) 3033
  13. E. D. van Ooijen, D. van Oosten and P. van der Straten, Debye Institute, Utrecht University, The Netherlands:
    14. Dynamical spectroscopy in an optical lattice. Using laser cooling, atoms can be produced with sufficiently low velocities to be trapped in optical potentials. The study of the dynamics of atoms in periodic potentials produced by interfering laser beams, displays a rich variety of new phenomena, which are closely related to the physics of the electron transport in crystals. These so-called optical lattices can be created in d dimensions using d + 1 intersecting laser beams, exploiting the light shift experienced by the atoms due to the nearly resonant light.

    One important parameter in these experiments is the filling factor of the lattice, i.e. the number of atoms per lattice site. Since the periodicity of an optical lattice is half the wavelength of the laser light, the density q = (Dx Dy Dz)-1 required to load a 3D lattice with one sodium atom per site is 1014 cm-3. Loading a 3D optical lattice from (for instance) a vapor-cell MOT with typical density of 1010 cm-3 results in a low filling factor.

    To achieve a high filling factor we have constructed a Magneto-Optical Trap (MOT) loaded from a decelerated atomic beam. To increase the density of the MOT we first use a Magneto-Optical Compressor (MOC) to focus and deflect the Zeeman-slowed atomic beam in the capture area of the MOT resulting in a higher loading rate and a lower loss rate. Furthermore, we use a Dark-MOT to increase the density even further. Finally, optical cooling in the lattice will be used to enhance the filling factor to the order of one atom per site.

    The setup will be used to study the effects of the optical potential on the dynamics of the atoms. For this we will use photo-association spectroscopy of the atoms, which probes the distribution of the atoms on the wavelength scale. Furthermore, we intend to study the phase transition of the atoms in the optical lattice from a conducting to an isolating phase, which has been predicted recently and has been studied theoretically in our group.
  14. Radmila Panajotovic, James P. Sullivan and Stephen J. Buckman, Australian National University:
    15. Experimental investigation of temporary negative ions in electron scattering from magnesium atoms. We present measurements of resonances observed in the differential elastic channel and in the excitation function for the 31P1 state in magnesium. Data has been collected for three different energy ranges: from 2 to 4 eV, from 4 eV to the first ionisation limit (7.644 eV), and above this limit. Measurements in the elastic scattering channel have been performed at four different angles (24o, 54o, 90o and 120o) and the excitation function has been observed via the radiative decay that occurs at a wavelength of 285.3 nm.
  15. Jamal Berakdar, Halle, Germany: On the many-body Green operator of few interacting particles.
    16. For the description of a quantum system we can solve the Schroedinger equation and obtain thus the spectrum of the system or one can equally derive the Green function of the system. In as much as it is difficult to solve the Schroedinger equation of a many-body interacting system, it is also cumbersome to derive the expression for the corresponding Green operator. This work develops an incremental, algebraic approach which deduces the Green and the transition operators of an interacting N body system from the solutions of the N-M body problem where M=1 ... (N-2). This cumulative, non-perturbative scheme is obtained via exact algebraic transformations of the Dyson equations. For numerical implementation an expansion of the Green operator is presented that can be truncated according to the desirable accuracy. The method is applied to three and four interacting Coulomb particles where the Green operator is obtained and the respective scattering spectrum is evaluated numerically. The calculated three and four particle continuum spectrum is in good accord with recent experimental findings. Further applications to doubly excited electronic states at surfaces are envisaged and the results of the two-particle spectrum will be presented at the conference.
  16. Max Colla, M. D. Hoogerland, L. Uhlmann, R. J. Gulley, K. J. H. Baldwin and S. J. Buckman, Australian National University:
    17. Low energy electron scattering from cold metastable helium atoms : total cross section measurements. For low energy electron scattering from metastable helium atoms, considerable discrepancies exist between experiments and the most recent theoretical calculations. We report on a new method for detailed measurements on this fundamentally important system. Atoms are cooled and trapped using laser cooling techniques, and the trap losses due to the interaction with a high current electron beam are recorded.
  17. J. Gambetta, K. Pregnell, N. Groothoff, R.T. Sang and W.R. MacGillivray, Griffith University, Queensland: Superelastic scattering from the 5P levels of atomic rubidium. The spin averaged wavefunction describing the excitation of ground state atom to an excited P state by electron collision, may be fully characterised by four atomic collision parameters [1]. Provided that the wavelength of the transition is accessible by current lasers, these parameters can be measured via the electron-atom superelastic scattering technique [2]. This technique involves the excitation of a ground state atom to an excited state with a laser of well defined polarisation. Subsequent to this laser excitation, the atom is induced to decay non-radiatively by electron induced impact back to the ground state. The electron gains the energy transferred in the collision, ie it is superelastically scattered. The measurement of these superelastically scattered electrons as a function of specific laser polarisations enable the determination of the atomic collision parameters.

    In the natural frame, the parameter rho00 is zero, unless there is an electron spin flip as a result of the collision. A non-zero rho00 indicates to a break-down of the LS coupling approximation [1,3]. If a spin flip, which is due to relativistic spin orbit mechanisms occurs, then the symmetry requirements of the collision are relaxed and the population of the symmetrically forbidden substate (mL) may result. In the case of atoms with heavy nuclei, it is predicted that relativistic effects will play a significant role. It was expected that electron - Rb collisions would exhibit a spin flip. However, a series of measurements by Hall et. al. with 20 eV incident energy electrons did not produce evidence of a non-zero rho00 over a significant angular range [4]. In this paper we will present the progress on a new series of experiments designed to measure the atomic collision parameters, in particular non-zero parameters, for electron - Rb collisions as a function of scattering angle for the higher incident electron energy of 40eV.

    [1] N. Andersen, J.W. Gallagher, and I.V. Hertel, Phys. Rep. 165, 1 (1988).
    [2] I.V. Hertel and W. Stoll, J. Phys. B: At. Mol. Phys. 7, 583 (1974).
    [3] R. P. McEachran, A.D. Stauffer, and V. Zeman, J. Phys. B: At. Mol. Phys. 30, 3475 (1997).
    [4] B.V. Hall, Y. Shen, A.J. Murray, I. Bray, W.R. MacGillivray and M.C. Standage, in preparation.

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